When to use the short form vs. long form
Bluebook Rule B10.2:
You can use the short form only if the full citation "falls in the same general discussion"**, is clear to the reader what is referenced, and the reader will have no difficulty locating the citation.
ALWD Rule 11.1c
Only have to use full cite the first time you cite to the source, but you CAN use full cite more frequently if local court rules require or the first time you you cite to a source in a new section of the document.
** Usually people interpret "in the same general discussion" as in the same "section" of the brief, like the ALWD rule says. However, "in the same general discussion" might be ambiguous if there are 2 or 3 very small subsections under a main section, and it would seem O.K. then to use the short form in the subsections. Just try and be consistent in interpreting the rules because they do afford some discretion.
In briefs (in text citing):
In Bluebook, you need to cite after every sentence that has information from a source and is not common knowledge or your opinion.
ALWD Rule 34.2: "When you refer to two or more sentences from the same page, section, or other subdivision of the same source within a single paragraph and there are no other intervening citations, you may place a single citation to the source at the end of the paragraph." However, the best practice is to cite after every sentence in order to avoid confusion.